In One Big Happiny Family!, while traveling on Cycling Road, the Egg began to glow. After taking it to a Pokémon Center and receiving assistance from Nurse Joy, the Egg hatched into Happiny. Soon after birth, she began crying for a stone to hold as a fake Egg. Brock found a white stone and polished it into an Oval Stone for her. Team Rocket snatched Happiny away before he could give the stone to her. Eventually, Happiny was returned to Brock and received her "Egg". Immediately after, she offered it back to Brock as a sign of friendship. He gave it back to her and then caught her in a Poké Ball.

As a Happiny

In Tanks for the Memories!, Happiny learned how to use Secret Power in order to save Autumn and Ilta from a group of Beedrill. She also used Secret Power later on in the episode to put Team Rocket to sleep so that Brock and Autumn could get away.

Brock was going to use Happiny in her first battle against Marilyn's Shellder in Battling a Cute Drama!. However, right before the battle started, Team Rocket interrupted and tried to steal Marilyn's other Pokémon. Before they could succeed, Happiny was able to send them flying with her powerful Pound attack.

In The Brockster Is In!, a group of Tentacruel attacked the boat that Ash and his friends were taking back to Twinleaf Town. Their Poison Sting attack caused many of the baby Pokémon to become poisoned. Despite all that Brock and the others were doing to help, they were not getting any better. After seeing this, Happiny evolved into Chansey in order to help the baby Pokémon. After evolving, she was able to heal Pichu and all of the baby Pokémon of the poison with her newly learned Soft-Boiled move.

Personality and characteristics

Chansey and Brock

Like most baby Pokémon, Happiny became very attached to her Trainer very quickly. She would become upset whenever she is taken out of Brock's care, and she refused to cooperate with Team Rocket completely. Unlike Bonsly, however, she did not cry and fuss; she actually fought back against Team Rocket's Pokémon after Brock had been hurt.

The only times where her strength was not enough were in Leading a Stray!, where she tried to pull off a tight manhole cover, but failed; and in The Psyduck Stops Here!, where she tried lifting a massive boulder, but collapsed under the weight and was knocked out. Any other time, she successfully brought out her special and uncommon power.